Be careful of the "Sticky Keys" thing. In recent Win versions at least, it's intentionally "augmented" to facilitate people with limited motion, fewer than usual fingers, or other such specialized personal attributes.

If, as leenia suggested, you check out Help [Start|Help] and look for "Accessibility" you'll find a whole blob of "very special features" that can be turned on/off. Sticky Keys is one of them, and there are - if I recall - a couple of different ways they can be turned on/off. There are also extra large text, magnifier views, and some little tricks for accomodating voice input programs and such. You can put a "keyboard" on screen that can be "moused" to type, completly (almost) eliminating the keyboard, if it's helpful.

There may be some things there that will be very helpful for Mum, but someone who knows Mum should look, and decide (in consultation with Mum, if possible) which ones will help and which ones will just get in the way.

John